Electric storage device

ABSTRACT

There is provided an electric storage device in which an electrode assembly enclosed in an insulating cover can be smoothly inserted in a case and the electrode assembly is positioned in place inside the case when housed in the case. The electric storage device according to the present invention includes an electrode assembly, an insulating cover covering the electrode assembly, and a case including a case body having a rectangular box shape and having an opening, the case body being configured to house the electrode assembly and the insulating cover, wherein the insulating cover is formed into a rectangular box shape conforming to the case body, and a portion of each of edges at which adjacent side surfaces of the insulating cover meet each other is beveled into a beveled part, the portion being close to the bottom of the insulating cover.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No.2010-293134, the disclosure of which is incorporated herein by referencein its entirety.

FIELD OF THE INVENTION

The present invention relates to an electric storage device, wherein anelectrode assembly to be housed in a case is covered with an insulatingcover, which insulates the electrode assembly from the case.

BACKGROUND ART

In recent years, rechargeable and dischargeable electric storage devicessuch as battery cells (e.g., a lithium ion battery cell and anickel-metal hydride battery cell) and capacitors (e.g., an electricdouble layer capacitor) have been adopted as the power sources ofvehicles (e.g., an automobile and a motorcycle) and various devices(e.g., a portable terminal and a laptop computer). For example, variousenergy-dense lithium secondary battery cells are made available as apower source for electric vehicles or the like. A lithium secondarybattery cell includes an electrode assembly housed in a metal case,electrode terminals projecting from inside the case to the outside ofthe case, a current collector which interconnects the electrode assemblyand electrode terminals, and an insulating cover disposed between thecase and the electrode assembly to insulate them.

Patent Document 1 (JP-A-2009-26704) describes a battery cell includingan electrode assembly (“electrode element” in Patent Document 1)designed to be easily insertable into a case (“outer case” in PatentDocument 1) and an insulating cover (“insulating film” in PatentDocument 1). In the battery cell, the electrode assembly 120 is insertedin the insulating cover 110 having the shape of a bag with an opening111, is then placed in an interior space 131 formed in the case 130 andis supported by the inner walls of the case 130 via the insulating cover110 as illustrated in FIG. 7.

Projecting sides 112, 112 are formed at both sides of the insulatingcover 110 by pressing both sides of the insulating cover 110 from twosides to integrate them together. Accordingly, the two projecting sides112 of the insulating cover 110 come into contact with the inner wallsof the case 130. This reduces friction resistance caused when theinsulating cover 110 is inserted into the case 130.

In the battery cell described in Patent Document 1, spaces as wide asthe widths of the projecting sides 112 are formed inside the case 130 bythe provision of the projecting sides 112 of the insulating cover 110.Furthermore, the spaces are formed to be longer than the projectingsides 112 so that the lower edges of the projecting sides 112 do not hitthe inner walls of the case 130 when the electrode assembly 120 housedin the insulating cover 110 is inserted into the case 130.

Accordingly, in the battery cell described in Patent Document 1described above, the electrode assembly 120 is not positioned in placeinside the case 130 simply by inserting the electrode assembly 120 intothe case 130. Consequently, the electrode assembly 120 can tilt so thatthe front and rear surfaces are at an angle with respect to the frontand rear surfaces of the case 130. In that case, the cover plate of thecase 130 to which the electrode assembly 120 is attached through thecurrent collector does not fit the opening of the case body of the case130. Accordingly, attaching the cover plate to the opening of the casebody of the case 130 becomes considerably troublesome. This problem canoccur with a capacitor (such as an electric double layer capacitor) aswell.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an electric storagedevice designed so that an electrode assembly covered with an insulatingcover can be smoothly inserted into a case and the electrode assembly ishoused and positioned in place in the case.

An electric storage device according to the present invention includes:

an electrode assembly;

an insulating cover covering the electrode assembly; and

a case comprising a case body having a rectangular box shape and havingan opening, the case body being configured to house the electrodeassembly and the insulating cover;

wherein the insulating cover is formed into a rectangular box shapeconforming to the case body; and

a portion of each of edges at which adjacent side surfaces of theinsulating cover meet each other is beveled into a beveled part, theportion being close to the bottom of the insulating cover.

In an embodiment of the present invention, the electric storage devicemay be configured in such a manner that:

the insulating cover includes: a bottom surface part; and a pair ofopposed principal surface parts and a pair of opposed edge surfaceparts, the principal surface parts and the edge surface parts risingfrom end edges of the bottom surface part; and

the insulating cover is formed by folding an insulating sheet.

In this case, the insulating sheet may include:

a first section that forms the bottom surface part;

a pair of second sections, projecting from a pair of opposed end edgesof the first section, the pair of second sections forming the pair ofprincipal surface parts; and

a pair of third sections forming the pair of edge surface parts, each ofthe third sections projecting from one of a pair of opposed side edgesof at least one of the pair of second sections.

Furthermore, in this case, the insulating sheet may have a boundarybetween the second section and the third section, a portion of theboundary close to the first section having a fold that forms the beveledpart.

Furthermore, in this case, the fold may be provided in plural, which arealigned parallel to each other along the boundary.

In another embodiment of the electric storage device according to thepresent invention, each of the pair of third sections may include apiece of the third section projecting from one of the pair of secondsections and another piece of the third section projecting from theother of the pair of second sections; and

the two pieces of the third section may overlap each other.

In this case, the overlapping two pieces of the third section may bejoined together.

Furthermore, in this case, the overlapping two pieces of the thirdsection may be joined together at a portion opposite from the firstsection.

In still another a embodiment of the present invention, the electricstorage device may further include:

a first current collector connected to the electrode assembly, the firstcurrent collector together with the electrode assembly being coveredwith the insulating cover,

wherein the insulating sheet further includes a first flap projectingfrom an end edge of at least one of the pair of second sections, thefirst flap to be inserted into a gap formed between the first currentcollector and the electrode assembly, the gap being at the opening ofthe case body.

In this case,

the electric storage device may further include a second currentcollector, wherein:

the electrode assembly includes a positive electrode plate and anegative electrode plate which are insulated from each other;

the first current collector is connected to the positive electrode plateand the second current collector is connected to the negative electrodeplate; and

the first flap is disposed in at least one of a position correspondingto the first current collector and a position corresponding to thesecond current collector.

Furthermore, in this case,

the flap may further include a second flap, the first flap may bedisposed in a position corresponding to the first current collector andthe second flap may be disposed in a position corresponding to thesecond current collector.

In yet another embodiment of the electric storage device according tothe present invention, embossing may be applied to the sheet entirely orpartially.

In another embodiment of the present invention, the electric storagedevice may further include:

first and second current collectors connected to the electrode assembly,the first and second current collectors together with the electrodeassembly being covered with the insulating cover,

wherein the electrode assembly includes a positive electrode plate and anegative electrode plate which are insulated from each other;

the first current collector is connected to the positive electrode plateand the second current collector is connected to the negative electrodeplate; and

each of the pair of edge surface parts of the insulating cover may besandwiched between an inner surface of the case body and a correspondingone of the first and the second current collectors.

In still another embodiment of the present invention, the electricstorage device may further include:

first and second current collectors connected to the electrode assembly,the first and second current collectors together with the electrodeassembly being covered with the insulating cover,

wherein the electrode assembly includes a positive electrode plate and anegative electrode plate which are insulated from each other;

the first current collector is connected to the positive electrode plateand the second current collector is connected to the negative electrodeplate; and

the two pieces of the third section of the insulating sheet overlap eachother along the current collector.

In yet another embodiment of the present invention, the electric storagedevice may further include:

a current collector connected to the electrode assembly, the currentcollector together with the electrode assembly being covered with theinsulating cover,

wherein the beveled part is located closer to the bottom of the casebody than a wide portion of the current collector.

In this case,

the wide portion of the current collector may be provided in a locationin a tip part of the current collector, the location being anintermediate location in the direction of the length of the currentcollector; and

the tip part of the current collector may gradually narrow from the wideportion toward a tip.

In another embodiment of the present invention, the electric storagedevice may further include:

a current collector connected to the electrode assembly, the currentcollector together with the electrode assembly being covered with theinsulating cover,

wherein the case includes the case body and a cover plate closing andsealing the opening of the case body; and

the current collector is fixed on an inner surface of the cover plate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional front view of a battery cell according tothe present invention,

FIG. 2 is a perspective view of an essential portion of the batterycell;

FIG. 3 is a plan view of a sheet to be made into an insulating coverwhich is included in the battery cell;

FIG. 4 is an enlarged view of embossing on the insulating cover;

FIG. 5 is an exploded perspective view of the battery cell;

FIG. 6 is front views of various forms of a current collector which isincluded in the battery cell; and

FIG. 7 is an exploded perspective view schematically illustrating aconventional battery cell.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A battery cell which is an embodiment of an electric storage deviceaccording to the present invention will be described below withreference to drawings. The battery cell according to this embodiment isa nonaqueous electrolyte secondary battery cell, more specifically, alithium-ion secondary battery cell. As illustrated in FIG. 1, thebattery cell according to this embodiment includes a case 1 made up of acase body 1 a and a cover plate 1 b which covers and seals an opening ofthe case body 1 a. A terminal structure 9 which is electricallyconnected to an electrode assembly 4 housed in the case 1 are providedin the cover plate 1 b.

The case body 1 a and the cover plate 1 b of the case 1 are made of ametal such as an aluminum alloy or steel. The case body 1 a has theshape of a rectangular box that is flat in the width direction, designedto house the winding type electrode assembly 4 having the shape of anellipsoidal cylinder. The cover plate 1 b is a rectangular plate thatfits the opening of the case body 1 a. The cover plate 1 b is fittedinto the opening of the case body 1 a and sealed and fixed by laserwelding or other technique. A gas discharge vent 3 is provided in thecenter of the cover plate 1 b.

In the electrode assembly 4, a band-shaped positive electrode plate 5and a band-shaped negative electrode plate 6 which are displaced to eachother in different lateral directions with a band-shaped separator 7sandwiched therebetween are wound about a lateral rotation axis into acylinder in the shape of a vertically long ellipse. The electrodeassembly 4 is entirely covered with an insulating cover comprising aninsulating sheet and is stored in the casing 1 while being insulatedfrom the casing 1.

The positive electrode plate 5 includes aluminum foil carrying apositive electrode active material at the surface. The negativeelectrode plate 6 includes copper foil carrying a negative electrodeactive material at the surface. The positive electrode plate 5 and thenegative electrode plate 6 each have a non-overlapped portion not coatedwith the active material at an edge in the lateral direction in whichthe sheet is displaced. With this arrangement, at the lateral ends ofthe electrode assembly 4, the aluminum foil and copper foil are exposed,and thus these metal foils of the positive electrode and negativeelectrode project from the overlapped portion in a wound configuration.

Metal foils projecting at the lateral ends of the electrode assembly 4are electrically connected to respective current collectors 8. Thecurrent collectors 8 are a conductive metal member bent into avertically long L-shape. More specifically, the current collector 8 forthe positive electrode comprises aluminum or an aluminum alloy, and thecurrent collector 8 for the negative electrode comprises copper or acopper alloy. The horizontal portion of the current collector 8 is afirst connection part 8 a. A gap is provided between the connection part8 a and the electrode assembly 4. The vertical portion of the currentcollector 8 is made up of an upper, intermediate part 8 b and a lower,second connection part 8 c which are continuous with each other.

The second connection part 8 c is one that is two-forked and bent to aright angle in such a manner that the edges face the electrode assembly4, or is one in which an opening is provided and two ridges are providedin such a manner that the edges face the electrode assembly 4. Thesecond connection part 8 c, together with an end of the electrodeassembly 4, is clamped by a clamp plate, not shown, and is connected andfixed by ultrasonic welding or other technique.

The terminal structure 9 includes a positive electrode terminalstructure 9 and a negative electrode terminal structure 9. Each terminalstructure 9 includes a plastic plate 10, an outer gasket 11 internallyand externally disposed to surround each of through-holes 1 c formed ateach of right and left ends of the cover plate 1 b, a rivet 12 insertedinto each through hole 1 c through the plastic plate 10 and the outergasket 11 and electrically connected to the connection part 8 a of thecurrent collector 8, a terminal retainer 13 disposed close to the outergasket 11, a terminal bolt 14 disposed on the outer surface of the coverplate 1 b through the terminal retainer 13, and a connection plate 15which electrically interconnects the terminal bolt 14 and the rivet 12.This arrangement electrically connects the electrode assembly 4 in thecase 1 to the terminal bolt 14.

The plastic plate 10, the outer gasket 11 and the terminal retainer 13represent an insulating member. In particular, the outer gasket 11 (andthe plastic plate 10 in some instances) also has a sealing function andtherefore represents an insulating and sealing member. The rivet 12represents an auxiliary terminal. The terminal bolt 14 represents anexternal terminal. The connection plate 15 represents connectionconductor. However, the terminal retainer 13 may not have insulatingproperties. When aluminum or an aluminum alloy is used as a material forthe case 1, the terminal retainer 13 of the positive electrode may benon-isolated so that the potential of the positive electrode may beidentical with the potential of the case 1. This suppresses corrosion ofthe case 1. When iron or stainless steel is used as a material for thecase 1, the terminal retainer 13 of the negative electrode may benon-isolated so that the potential of the negative electrode may beidentical with the potential of the case 1.

The insulating cover 2 will now be described with reference to FIG. 2.The insulating cover 2 includes a rectangular bottom surface part 2 abetween the bottom plate of the case body 1 a and the bottom of theelectrode assembly 4, a pair of opposed principal surface parts 2 b, 2 brising from end edges of the bottom surface part 2 a, and a pair of edgesurface parts 2 c, 2 c, and is formed into the shape of a rectangularbox conforming to the shape of the case body 1 a. A part of the boundarybetween each principal surface 2 b and each edge surface part 2 c of theinsulating cover 2 that is near the bottom constitutes a beveled part 2d. The boundary between each principal surface 2 b and each edge surface2 c except the beveled part 2 d is a sharp edge (unbeveled part) 2 e.For example, the beveled part 2 d is 13% of the boundary between theprincipal surface 2 b and the edge surface 2 c and the sharp edge 2 e is87% of the boundary between the principal surface 2 b and the edgesurface 2 c. The bottom surface part 2 a constitutes the bottom of theinsulating cover 2. The pair of principal surface parts 2 b, 2 b and thepair of the surfaces 2 c, 2 c constitute the side surfaces of theinsulating cover 2.

The insulating cover 2 is formed from a sheet 20 illustrated in FIG. 3.The sheet 20 includes a rectangular section (hereinafter referred to asthe “first section”) 21 that forms the bottom surface part 2 a, sections(hereinafter referred to as the “second sections”) 22, 22 that projectfrom a pair of opposed end edges (boundaries) 20 a, 20 a at the longersides of the first section 21 and form the principal surface parts 2 b,2 b, projecting parts 24, 24 projecting from end edges (boundaries) 20b, 20 b at the opposed pair of shorter sides of the first section 21,sections (hereinafter referred to as the “third sections”) 23, 23 thatproject from the both side edges 20 c, 20 c of the second sections 22and forms the edge surface parts 2 c, 2 c, and two flaps 25, 25,projecting from the outer edge 20 d of one of the second sections 22,22.

The first section 21 has the same size as the inner surface of thebottom plate of the case body 1 a. Each of the third sections 23 has thesame width as the inner surface of the edge plate of the case body 1 a.The length of each of the projecting parts 24 projecting from the firstsection 21 is equal to the width of the third section 23.

The width of each of the flaps 25 projecting from the outer edge 20 d ofone of the second sections 22 is smaller than the width of the firstsection 21. It should be noted that the flaps 25 do not necessarily needto project from one of the second sections 22; although not depicted,one of the flaps 25 may project from one of the second section 22 andthe other flap 25 may project from the other second section 22, providedthat the two flaps 25 are paired correspondingly to the positiveelectrode and negative electrode terminal structures 9 and a blank part29 is provided between the flaps 25.

Two folds 26 a, 26 b are formed on the first section 21 side of theboundary between the second section 22 and the third section 23 toprovide the beveled part 2 d. The folds 26 a, 26 b are formed along theboundary. The number of the folds is not limited to two. What isrequired is that a plurality of folds 26 b, . . . are provided so thatthe beveled part 2 d is formed. A notch 27 is formed from between thethird section 23 and the projecting part 24 to the folds 26 a formed inthe second section 22. A tear-preventing cut 28 is formed at theboundary between the flap 25 and the second section 22 to prevent thesheet 20 from being torn.

As illustrated in FIG. 4, embossing E is applied to one or both of thesurfaces of the sheet 20 entirely or partially. The embossing E isapplied in such a manner that ridges Eb are extended from points of eachprotuberance Ea having the shape of a quadrangular frustum pyramid.Furthermore, the embossing E can be accomplished on both surfaces of thesheet 20 by depressing portions of the sheet 20 from one side and thendepressing the regions adjacent to the portions from the other side.

It should be noted that when the unfolded sheets 20 are stacked andstored, the embossing E applied to one or both side of the sheets 20prevents the stacked sheets 20 from sticking to each other. To preventsticking, the embossing E needs to be applied to only one side of thesheet. However, preferably the embossing E is applied to both sidesbecause the sheet 20 is likely to curl if only one side is embossed.

As illustrated in FIG. 5, the sheet 20 is folded along the boundaries 20a, 20 a between the first section 21 and the second sections 22, 22 intoa U-shape as seen from the side. The third section 23 projecting fromone of the second sections 22 is folded along the side edge 20 c and thethird section 23 projecting from the other second section 22 is foldedalong the side edge 20 c, then the third section 23 projecting from oneof the second sections 22 and the third sections 23 projecting from theother second section 22 overlap each other. When the third sections 23are folded, the third sections and the second sections 22 are alsofolded along the folds 26 a, 26 b to form the beveled parts 2 d.

Portions of the overlapping third sections 23, 23 close to the open end(the upper portions in FIG. 5), that is, portions of the overlappingthird sections 23, 23 opposite from the beveled parts 2 d, are sealed,for example heat-sealed by point sealing (cf., symbol S in FIG. 2). As aresult, the sheet 20 is formed into the shape of a thin container and isprevented from unfolding. The electrode assembly 4 is inserted into thesheet 20 formed into the thin container. It should be noted that theentire length of the third sections 23 may be sealed.

Alternatively, the electrode assembly 4 may be placed in the sheet 20when it is folded into a U-shape as seen from the side, so as to besandwiched between the second sections 22, 22. Alternatively, theelectrode assembly 4 may be placed on the first section 21 and then thesecond sections 22, 22 may be folded so that the electrode assembly 4 issandwiched between the second sections 22, 22. In these cases, then thethird sections 23, 23, . . . are folded so that the third section 23, 23overlap each other along the vertical part of the current collector 8.Then, portions of the overlapping third sections 23, 23 on the open endside are sealed, for example heat-sealed together by point sealing whileusing the intermediate part 8 b of the current collector 8 as a pad(cf., symbol S in FIG. 2). This prevents the sheet 20 from unfolding.

In any of the cases, the two flaps 25, 25 project from the secondsection 22 of the sheet 20 enclosing the electrode assembly 4. Each flap25 is inserted in the gap between the connection part 8 a of the currentcollector 8 and the electrode assembly 4. A blank part 29 is providedbetween the two flaps 25, 25 so that the gas discharge vent 3 is notcovered by the flaps 25, 25. The projecting parts 24, 24 project fromthe first section 21.

The electrode assembly 4 covered with the sheet 20 in this manner isinserted into the case body 1 a. As the electrode assembly 4 isinserted, the projecting parts 24, 24 are forcedly bent by the edges ofthe opening of the case body 1 a to overlap the third sections 23, 23and become part of the side surfaces 2 c of the insulating cover 2. Theprovision of the beveled parts 2 d near the bottom surface part 2 a ofthe insulating cover 2 facilitates smooth insertion into the case body 1a. Thus, the electrode assembly 4 is smoothly inserted into the casebody 1 a.

Furthermore, the embossing E applied to the surface of the sheet of theinsulating cover 2 reduces the contact friction between the inner wallsof the case body 1 a and the insulating cover 2. Accordingly, theelectrode assembly 4 can be smoothly inserted into the case body 1 a.

The edges 2 e, . . . of the insulating cover 2 are in contact with (theedges of) the inner walls of the case body 1 a when the electrodeassembly 4 is fully housed in the case body 1 a. The end surface parts 2c of the insulating cover 2 are sandwiched between the edge plates ofthe case body 1 a and (the vertical parts of) the current collector 8 intight or substantially tight contact. Accordingly, the electrodeassembly 4 is positioned in place in the case body 1 a when housed inthe case body 1 a. Consequently, the cover plate 1 b can be easilyjoined to the opening of the case body 1 a during manufacturing of thebattery cell.

As has been described above, in the battery cell according to thisembodiment, the beveled parts 2 d, . . . are provided in the portions ofthe edges 2 e, . . . between the adjacent side surfaces of theinsulating cover 2 that are near the bottom of the insulating cover 2.This facilitates smooth insertion of the electrode assembly 4 into thecase body 1 a. Furthermore, when the electrode assembly 4 covered withthe insulating cover 2 is housed in the case body 1 a, the edges 2 e, .. . of the insulating cover 2 at which the adjacent side surfaces meeteach other are in contact with the inner surfaces of the case body 1 a,except the beveled parts 2 d, . . . . Accordingly, the electrodeassembly 4 can be positioned in place in the case body 1 a when housedin the case body 1 a.

In the battery cell according to this embodiment, the insulating cover 2is formed by folding the insulating sheet 20. This allows the electrodeassembly 4 to be easily covered (enclosed).

In the battery cell according to this embodiment, the overlapping thirdsections 23, 23 are sealed together. This prevents the sheet 20 formedinto a predetermined shape from unfolding. Because the sheet 20 does notunfold, the electrode assembly 4 covered with the sheet 20 can be easilyinserted into the case body 1 a.

Portions of the overlapping third sections 23, 23 close to the open end,that is, portions of the overlapping pieces of the third section 23, 23opposite from the first sections 21, are sealed. Accordingly, the thirdsection 23 projecting from one of the second sections 22 and the thirdsection 23 projecting from the other second section 22 are out of linewith each other in the direction of the width of the edge surface 2 cwhen overlapping and being sealed, making the width of the edge surfaceparts 2 c of the insulating cover 2 larger than the inside width of thecase body 1 a. Consequently, elastic resilience in the width directionis added to the insulating cover 2. This ensures the contact of theinsulating cover 2 with the inner surfaces of the case body 1 a.

Furthermore, in the battery cell according to this embodiment, the flaps25 of the insulating cover 2 are inserted in the gap formed between theelectrode assembly 4 and the first connection parts 8 a of the currentcollector 8 (more specifically, the lower parts of the rivets 12functioning as auxiliary terminals). Thus, the buffering effect of theflaps 25 can prevent damage and a short circuit of the electrodeassembly 4 if the battery cell is so vigorously vibrated that the lowerparts of the auxiliary terminals 12 and the electrode assembly 4 may hitagainst each other.

The vertical part of the current collector 8 has a wide portion 8 d atthe lower end (tip part) as illustrated in the left-hand part of FIG. 6.The lower end (tip part) of the current collector 8 gradually narrowsfrom the wide portion 8 d. Each of the beveled parts 2 d of theinsulating cover 2 is located nearer to the bottom of the case body 1 athan the wide portion 8 d. Accordingly, the wide portion 8 d of thecurrent collector 8 does not hit the inner surfaces of the beveled parts2 d of the insulating cover 2. Therefore, the electrode assembly 4connected with the current collector 8 can be easily inserted into theinsulating cover 2. This advantageous effect is also produced by theshape of a current collector 8′ (wide portion 8 d′) illustrated in themiddle part of FIG. 6 and the shape of a current collector 8″ (wideportion 8 d″) illustrated in the right-hand part of FIG. 6.

The present invention is not limited to the embodiments described above;various modifications may be made without departing from the spirit ofthe present invention.

For example, the insulating cover 2 may be configured to be housed inthe case body 1 a without heat-sealing the overlapping third sections23, 23. Furthermore, the third sections 23, 23 do not necessarily needto be sealed together. For example, the third sections 23, 23 may beadhered to each other. Moreover, the embossing E is not essential.

The insulating cover 2 does not necessarily need to be formed from asheet 20 like the one illustrated in FIG. 3. Furthermore, if the gasdischarge vent 3 is provided in a plate of the case body 1 a rather thanin the cover plate 1 b, one elongated flap 25 may be provided ratherthan the two flaps 25.

The shape of the case body 1 a does not necessarily need to be a flatrectangular box shape one side of which is longer than the other; thecase body 1 a may have the shape of a square box.

The electrode assembly is not limited to the winding type having theshape of an ellipsoidal cylinder described above; the electrode assemblymay have any shape and may be of multilayered type.

While the embodiments have been described with respect to a lithium-ionbattery cell, the present invention can be applied to battery cells ofany type and size (capacity).

The present invention is not limited to lithium-ion secondary batterycells. The present invention can be applied to various secondary batterycells and primary battery cells, and capacitors such as electricaldouble layer capacitors.

1. An electric storage device comprising: an electrode assembly: an insulating cover covering the electrode assembly; and a case comprising a case body having a rectangular box shape and having an opening, the case body being configured to house the electrode assembly and the insulating cover; wherein the insulating cover is formed into a rectangular box shape conforming to the case body; and a portion of each of edges at which adjacent side surfaces of the insulating cover meet each other is beveled into a beveled part, the portion being close to the bottom of the insulating cover.
 2. The electric storage device according to claim 1, wherein the insulating cover comprises: a bottom surface part; and a pair of opposed principal surface parts and a pair of opposed edge surface parts, the principal surface parts and the edge surface parts rising from end edges of the bottom surface part, and the insulating cover is formed by folding an insulating sheet.
 3. The electric storage device according to claim 2, wherein the insulating sheet comprises: a first section that forms the bottom surface part; a pair of second sections, projecting from a pair of opposed end edges of the first section, the pair of second sections forming the pair of principal surface parts; and a pair of third sections forming the pair of edge surface parts, each of the third sections projecting from one of a pair of opposed side edges of at least one of the pair of second sections.
 4. The electric storage device according to claim 3, wherein the insulating sheet has a boundary between the second section and the third section, a portion of the boundary close to the first section having a fold that forms the beveled part.
 5. The electric storage device according to claim 4, wherein the fold is provided in plural, which are aligned parallel to each other along the boundary.
 6. The electric storage device according to claim 3, wherein each of the pair of third sections comprises a piece of the third section projecting from one of the pair of second sections and another piece of the third section projecting from the other of the pair of second sections; and the two pieces of the third section overlap each other.
 7. The electric storage device according to claim 6, wherein the overlapping two pieces of the third section are joined together.
 8. The electric storage device according to claim 7, wherein the overlapping two pieces of the third section are joined together at a portion opposite from the first section.
 9. The electric storage device according to claim 3, further comprising: a first current collector electrically connected to the electrode assembly, the first current collector together with the electrode assembly being covered with the insulating cover, wherein the insulating sheet further comprises a first flap projecting from an end edge of at least one of the pair of second sections, the first flap to be inserted into a gap formed between the first current collector and the electrode assembly, the gap being at the opening of the case body.
 10. The electric storage device according to claim 9, further comprising a second current collector, wherein: the electrode assembly comprises a positive electrode plate and a negative electrode plate which are insulated from each other; the first current collector is connected to the positive electrode plate and the second current collector is connected to the negative electrode plate; and the first flap is disposed in at least one of a position corresponding to the first current collector and a position corresponding to the second current collector.
 11. The electric storage device according to claim 9, wherein the flap further comprises a second flap, the first flap is disposed in a position corresponding to the first current collector and the second flap is disposed in a position corresponding to the second current collector.
 12. The electric storage device according to claim 2, wherein embossing is applied to the insulating sheet entirely or partially.
 13. The electric storage device according to claim 2, further comprising: first and second current collectors electrically connected to the electrode assembly, the first and second current collectors together with the electrode assembly being covered with the insulating cover, wherein the electrode assembly comprises a positive electrode plate and a negative electrode plate which are insulated from each other; the first current collector is connected to the positive electrode plate and the second current collector is connected to the negative electrode plate; and each of the pair of edge surface parts of the insulating cover is sandwiched between an inner surface of the case body and a corresponding one of the first and second current collectors.
 14. The electric storage device according to claim 6, further comprising: first and second current collectors electrically connected to the electrode assembly, the first and second current collectors together with the electrode assembly being covered with the insulating cover, wherein the electrode assembly comprises a positive electrode plate and a negative electrode plate which are insulated from each other; the first current collector is connected to the positive electrode plate and the second current collector is connected to the negative electrode plate; and the two pieces of the third section of the insulating sheet overlap each other along the current collector.
 15. The electric storage device according to claim 1, further comprising: a current collector electrically connected to the electrode assembly, the current collector together with the electrode assembly being covered with the insulating cover, wherein the beveled part is located closer to the bottom of the case body than a wide portion of the current collector.
 16. The electric storage device according to claim 15, wherein: the wide portion of the current collector is provided in a location in a tip part of the current collector, the location being an intermediate location in the direction of the length of the current collector; and the tip part of the current collector gradually narrows from the wide portion toward a tip.
 17. The electric storage device according to claim 1, further comprising: a current collector electrically connected to the electrode assembly, the current collector together with the electrode assembly being covered with the insulating cover, wherein the case comprises the case body and a cover plate closing and sealing the opening of the case body; and the current collector is fixed on an inner surface of the cover plate. 